The present invention relates to a method and an apparatus for cutting insulating materials. In particular, the present invention is directed to cutting quartz crystal plates for use in electromechanical filters and resonators.
Wire electro-erosion machining is a known process for cutting conducting materials by means of a wire electrode. In such a known method and apparatus, a continuously moving copper wire is positioned proximate to the conducting material to be cut. A difference in potential is imposed between the wire and the material while a liquid solution, e.g., deionized water, is fed coaxially to the wire. A multitude of electric discharges occurs between the wire and the material causing a cut in such material by electro-erosion. This known technique results in a contact-free machining process without exerting force on the conducting material. Simple as well as complex patterns can be achieved in accordance with this prior art arrangement. However, the latter is limited in its applicability to conducting workpieces made, for example, of steel or copper. This known method is inapplicable for cutting insulating materials such as quartz plates.
A known method for cutting piezoelectric crystals is described by W. P. Mason in "Piezoelectric Crystals and their Application to Ultrasonics", 1950, pages 167-168. In accordance with this method, cutting is performed by a wet-string type saw consisting of a plurality of endless strings running over pulleys. After cutting a crystal, the edges of such formed crystal plates must be ground to give a flat and straight edge finish. This method is adequate for cutting crystal plates. However, the frequency of such plates must be further adjusted by modifying the plates' dimensions. In other words, this prior art method and apparatus provides rough or uneven cuts and may cause undesirable stresses in the crystal. Although such a known method is acceptable for certain applications, it cannot be easily used where a very thin plate of quartz has to be cut in accordance with a predetermined pattern.